The 3rd-Generation Partnership Project (3GPP) continues to develop specifications for the fourth-generation wireless communication system known as “Long Term Evolution” or “LTE.” LTE uses Orthogonal Frequency-Division Multiplexing (OFDM) in the downlink (transmissions from base station to mobile terminal) and Discrete Fourier Transform (DFT)-spread OFDM in the uplink (transmissions from mobile terminal to base station). The basic LTE downlink physical resource can thus be seen as a time-frequency grid, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval.
In the time domain, LTE downlink transmissions are organized into radio frames of 10 milliseconds, each radio frame consisting of ten equally-sized subframes of length Tsubframe=1 millisecond. Resource allocation in LTE is typically described in terms of resource blocks, where a resource block corresponds to one slot (0.5 milliseconds) in the time domain and 12 contiguous subcarriers in the frequency domain. A pair of two adjacent resource blocks in time direction (1.0 millisecond) is known as a resource block pair. Resource blocks are numbered in the frequency domain, starting with the number 0 at one end of the system bandwidth.
Downlink transmissions in LTE are dynamically scheduled, which means that in each subframe the base station transmits control information identifying those terminals to which data is transmitted and identifying the resource blocks in which the data is transmitted, for the current downlink subframe. This control signaling is typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in each subframe, via a channel known as the Physical Downlink Control Channel (PDCCH). The particular number of symbols dedicated to the control channel region in each subframe (n=1, 2, 3 or 4) is specified by a Control Format Indicator (CFI). The downlink subframe also contains common reference symbols, which are known to the receiver and used for coherent demodulation of e.g. the control information. A downlink system with CFI=3 OFDM symbols used for the control region is illustrated in FIG. 1.
As of Release 11 of the 3GPP specifications for LTE, the above-described resource assignments can also be scheduled on an enhanced Physical Downlink Control Channel (EPDCCH). Unlike the PDCCH, the EPDCCH is mapped to resource elements in the data region of the downlink subframe, i.e., to those resource elements that are not in the control region and that are not used for reference symbols, synchronization signals, and the like. For systems and equipment that are compliant only to earlier releases (Releases 8 to 10) of the 3GPP specifications for LTE, only the PDCCH is available for scheduling of resource assignments.